1. Field of the Invention
The present invention relates to a technical field of a hydraulic pressure type booster in which an inputted power is increased to a predetermined value by the action of hydraulic pressure. More particularly, the present invention relates to a technical field of a hydraulic pressure type booster which is formed compact and the structure of which is simplified.
2. Description of the Related Art
In a hydraulic pressure type booster used for a servo assisted brake of an automobile, a high intensity output can be obtained by a low intensity input. An example of this hydraulic pressure type booster incorporated into a brake system of an automobile is disclosed in Japanese Utility Model Application No. 4-33402 (Japanese Unexamined Utility Model Publication No. 5-84553).
FIG. 4 is a view of the hydraulic pressure type booster. In the view, reference numeral 1' is a hydraulic pressure type booster, reference numeral 2' is a housing, reference numeral 3' is a plug, reference numeral 4' is a power piston, reference numeral 5' is a control valve, reference numeral 6' is a valve seat member, reference numeral 7' is a cylindrical fixing member, reference numeral 8' is a nut, reference numeral 9' is a ball valve, reference numeral 10' is a valve body, reference numeral 11' is a cylindrical member, reference numeral 12' is an input shaft, reference numeral 13' is a cylindrical stopper member, reference numeral 14' is a reaction force piston, reference numeral 15' is a power chamber, and reference numeral 16' is an output shaft.
In this hydraulic pressure type booster 1', when it is not operated as shown in FIG. 4, the ball valve 9' of the control valve 5' is seated on the valve seat member 6', and a front end valve portion of the cylindrical member 11' is unseated from the ball valve 9'. Therefore, the power chamber 15' is shut off from an input port 17' which is always connected to a hydraulic pressure source not shown in the view. At the same time, the power chamber 15' is communicated with a chamber 18' which is always connected to a reservoir not shown in the view. Accordingly, no hydraulic pressure is introduced into the power chamber 15', and the power piston 4' is not operated.
When an input is given to the booster which is in the above non-operating condition, the input shaft 12' is moved forward. Then the cylindrical member 11' is also moved forward, and the front end valve portion of the cylindrical member 11' comes into contact with the ball valve 9' of the control valve 5', and the ball valve 9' is pushed, so that the ball valve 9' is unseated from the valve seat member 6'. Due to the foregoing, the power chamber 15' is communicated with the input port 17' and shut off from the chamber 18'. Therefore, hydraulic fluid is introduced into the power chamber 15', and the power piston 4' is operated. When the power piston 4' is operated, power is outputted from the output shaft 16' of the hydraulic pressure type booster 1'. Therefore, a piston of a master cylinder (not shown) is operated, and the master cylinder generates a braking hydraulic pressure. When the hydraulic pressure in the power chamber 15' is increased to a predetermined value, the ball valve 9' is seated on the valve seat member 6'. Therefore, an input of the hydraulic type booster 1' is multiplied, and an output of the hydraulic type booster 1' becomes the multiplied value.
The reaction force piston 14' is pushed backward by the hydraulic pressure in the power chamber 15', resisting a force generated by the spring 19'. In the initial stage in which hydraulic pressure in the power chamber 15' is still low, the reaction force piston 14' does not come into contact with a step portion 12'a of the input shaft 12'. Accordingly, a multiplying factor of the hydraulic pressure type booster is high, and the jumping action is conducted. When hydraulic pressure in the power chamber 15' is increased to a predetermined value, the reaction force piston 14' comes into contact with the step portion 12'a of the input shaft 12'. After that, the multiplying factor of the hydraulic pressure type booster decreases and becomes a normal value.
When no input is given to the hydraulic pressure type booster, the input shaft 12' is retracted by a return spring, not shown in the drawing. Therefore, the cylindrical member 11' is also retracted, and the front end valve portion of the cylindrical member 11' is unseated from the ball valve 9' of the control valve 5'. Due to the foregoing, the power chamber 15' is shut off from the input port 17 and communicated with the chamber 18'. Therefore, hydraulic pressure introduced into the power chamber 15' is discharged into the reservoir, and the power piston 4' is retracted by the action of the return spring 20'. When the cylindrical stopper member 13' fixed to the input shaft 12' comes into contact with the stopper 25' of the plug 3', the input shaft 12' can not be retracted any more, that is, the input shaft 12' reaches a limit of retraction, and the hydraulic pressure type booster returns to the non-operating condition shown in the view. When hydraulic pressure introduced into the power chamber 15' is completely discharged, the power piston 4' also returns to the non-operating condition shown in the drawing. Therefore, no output is provided by the hydraulic pressure type booster 1' and the master cylinder is also put into a non-operating condition.
However, in the above conventional hydraulic pressure type booster 1', there are respectively provided O rings 22', 23', 24' for holding hydraulic tightness between an outer circumference of the collar 21' for slidably holding the valve body 10' to hold the ball valve 9' and the hole of the power piston 4' in which the collar 21' is engaged, and also between an outer circumference of the valve seat member 6' and the hole of the power piston 4' in which the valve seat member 6 is engaged, and also between an outer circumference of the plug 3' and the hole of the housing 2' in which the plug 3' is engaged.
Accordingly, the following problems maybe encountered. Outer diameters of the collar 21', valve seat member 6' and plug 3', to which O rings 22', 23', 24' are respectively attached, become large, and their lengths in the axial direction become long. Due to the foregoing, dimensions of the hydraulic pressure type booster 1' are increased.
Since the cylindrical member 11' is inserted and fixed to the cylindrical stopper member 13', the structure becomes complicated, and further fluctuation is caused in a clearance between the ball valve 9' and the front end valve portion of the cylindrical member 11'.
Further, the cylindrical fixing member 7' is fixed to the power piston 4' with the nut 8'. Therefore, length of the power piston 4' is increased because of this nut 8'. In other words, not only the length of the hydraulic pressure type booster 1' is increased in the axial direction, but also its assembling work becomes complicated.